Electrochemical and microbiological characterization of single carbon granules in a multi-anode microbial fuel cell

Capacitive microbial fuel cells (MFCs) use bacteria on a capacitive anode to oxidize organics in wastewater and simultaneously charge the electrode. This study aims to gain knowledge on the performance of single activated carbon (AC) granules, which are used as capacitive bioanodes. To this end, a multi-anode MFC that allows the testing of up to 29 granules under the same experimental conditions is used. 2 types of AC granules (PK and GAC) and 3 different size-ranges (n = 8 each) are studied in terms of current production, biomass quantification, microbial community and charge storage. Additionally, charge storage of PK granules (n = 24) is determined for different charging/discharging times. Results show that total produced charge directly relates to biomass amount, which has a linear relation towards granule outer surface area. Small AC granules have higher volumetric current densities, which could be of interest for their application in up-scaled reactors. PK granules show slightly higher biomass and current production than GAC granules, while these latter ones show larger volumetric charge storage capacity. Similarly, it is shown that short charging/discharging times are needed to obtain maximum charge storage and current output. These findings are of importance to design and operate MFCs with capacitive properties.